MAPT and Alzheimer disease: CSF levels of sTREM2 fall significantly in early pre-symptomatic stages prior to AD diagnosis (when amyloid is aggregating), but rise during mild cognitive impairment (MCI) and AD (when tau is aggregating), and fall again during the dementia stages of AD (Heslegrave et al., 2016; Piccio et al., 2016; Suárez-Calvet et al., 2016, 2019; Bekris et al., 2018; Liu et al., 2018; Nordengen et al., 2019; Rauchmann et al., 2019; Ma et al., 2020).